Stereo Steering Column Controls In 2000 Focus

i have a 2000 Focus with an rds 5000 stereo unit. Cd mulithcnager fitted ( and working ) and also the steering column controls fitted ( but NOT working ).

i have a 'spare' plug behind the stereo,which doesnt plug in anywhere,as i dont have a spare slot on the back of the stereo.I had a look at the back of an rds 6000 and i couldnt see any extra ports but apparantly these support cd multichangers and remote steering controls.

i think this 'spare' plug is the remote control,and i think that it isnt working,as its not plugged into the stereo anywhere.Are there 6000's with an extra port to plug this into , or can i remove the plug and put the wires into one of the existing connections.